Nitrate Losses From Disturbed Forests: Patterns and Mechanisms

Abstract

Abstract Losses of nitrate in drainage water from disturbed forest ecosystems vary over a wide range. High losses of nitrate to streamwater or groundwater have been observed in a few sites, while in others only small increases in losses have occurred. A limited set of mechanisms could be responsible for such differences. Before disturbance, annual nitrogen mineralization and plant nitrogen uptake vary widely among temperate forests, with higher rates observed in deciduous forests. Destructive disturbance increases nitrogen mineralization and (at least briefly) reduces plant uptake. The nitrogen mineralized in excess of plant uptake could be lost to streamwater or groundwater, lost to the atmosphere through ammonia volatilization or denitrification, or retained within the disturbed system through nitrogen immobilization by decomposers, clay fixation of ammonium, lags in nitrification, nitrate reduction to ammonium, nitrate adsorption on soil colloids, a lack of water for nitrate transport, or (once plant regrowth is established) plant nitrogen uptake. Systematic studies of these mechanisms will allow the development of a more thorough understanding of the nitrogen cycle in disturbed ecosystems. Such an understanding should in turn permit the prediction of nitrate losses from distrubed forests. Forest Sci. 25:605-619.